Various events affect the operation of vehicles, such as trucks and railroad cars, and the safety of their cargoes. For example, vehicles and their respective cargoes, are subject to substantial shocks from sources such as rear and front impacts, out of round wheels, unbalanced wheels, and "hunting" of "trucks" which carry a railroad car's wheels. In railroad cars, efforts are made to limit damage from shocks by means of cushioning units mounted between cars. As long as these operate properly they help protect the railroad car and its cargo from the impacts that occur when cars are coupled together or from "intrain" forces that occur when the train is being pulled along the tracks.
In order to keep vehicles operating properly, it is desirable to obtain information, either in the vehicle, or at a remote locating or both, concerning events that affect the vehicle operation.